PRACTICAL ORGANIC CHEMISTRY Quantitative Hydrolysis of Ethyl Benzoate.The quantitative estimation of an ester by hydrolysis is conducted as follows : a standard half-normal solution of alcoholic potash is prepared by dissolving 7 grams of caustic potash in about an equal weight of water and diluting to 250 c.c. with absolute alcohol. The liquid is allowed to stand overnight in a stoppered flask and filtered through asbestos into a clean diy bottle closed with a cork through which a 25 c.c. pipette is inserted. The solution is first standardised by titration against half- normal sulphuric acid, using phenol- phthalein as indicator. About I gram of ethyl benzoate is carefully weighed by difference by means of the ap- paratus shown in Fig. 82. A volume corresponding to about I gram is delivered into a- round flask (200 c.c.) by attaching a piece of rubber tubing to the wide end of the apparatus and blowing until the liquid descends to the required graduation on the wide limb. Twenty-five c.c. of the standard alcoholic potash solution is added, and the mixture boiled on the water-bath with reflux condenser for twenty minutes. FIG. 82. The amount of free alkali is estimated by titration with standard sulphuric acid and the quantity of ester calculated. Example.1'355 grams required 15'! c. c. N/2H2S04 15-1 XQ-I50X 100 2x1-1355 See Appendix^ p. 308. " = 997 per cent. PREPARATION 100. ff Acetophenone (Phenylmethylketone, Hypnone), C6H6.CO.CH3 . Friedel, Crafts, Ann. Chim. Phys., 1884, 1, 507 ; 14, 455. 30 grms. benzene. 50 aluminium chloride (anhydrous). 35 acetyl chloride.